Input pins:
- 0V
- +5V
- Display Voltage (ca. 1V?)
- RS (Register Select): raise to access display RAM, lower to access controller RAM
- RW (Read/Write Select): raise to read from RAM, lower to write to RAM
- E (Enable): LCD sends data on rising edge, reads data on falling edge
- data 0
- ...
- data 7
Initializing 4bit mode
The LCD can be interfaced using all 8 data pins, or alternatively using just pins 4,5,6,7. I chose to use 4-bit-mode, because this way I had to use less output pins of my microcontroller.I used the following sequence:
Rise E (as LCD will read on falling edge) Lower R/W (Write mode) Lower RS (instruction mode) Transmit high nibble of "8bit mode" three times Set output pins to "0011" (pins 4-7 on LCD!) Lower E Rise E Wait some ms Transmit high nibble of "4bit mode" once Set output pins to "0010" (pins 4-7 on LCD!) Lower E Rise E Wait some msThis sequence will switch back to 8bit mode (if the LCD has already been initialized) and then enter 4bit mode.
Transmitting data
To transmit 8bit data in 4bit mode we will transmit the upper 4 bits first, then the lower 4 bits.I used the following sequence:
Save old status of RS Transmit high nibble of data to be sent Lower E Rise E Transmit low nibble of data to be sent Lower E Rise E Rise R/W (we read...) Lower RS (...in instruction mode) (E is still high, so the LCD will immediately transmit the status of the busy flag) Wait while LCD is busy (bit 7 of status data is high) Receive high nibble of status data Lower E Rise E Receive low nibble of status data Lower E Rise E Wait some ms Restore old status of RS Lower R/W (back to write mode)
Initializing the display
To initialize the display I sent the following data:"0010 1000" - Multi-line-mode "0000 1100" - Display on "0000 0001" - Clear display "0000 0110" - LTR output